The invention relates to steering systems for boats, e.g., waterjet driven boats.
Waterjet boats are propelled by drawing a stream of water through a channel in the bottom of the boat and ejecting the stream out the back of the boat. A typical waterjet has two steering components: a nozzle and a reversing bucket. The nozzle is a tubular element near the rear of the propulsion stream (xe2x80x9cthe jetxe2x80x9d) that rotates from side to side. Rotating the nozzle deflects the exiting stream, imparting a side component to the propulsion vector, thereby turning the boat to port (left) or to starboard (right). A nozzle in a waterjet boat essentially serves the same purpose as a rudder in a propeller driven boat.
The reversing bucket allows an operator to slow or back up the boat. The bucket is a curved element located at the aftmost portion of the jet, just behind the nozzle. Ordinarily, the bucket is elevated above the jet, and has no effect on the operation of the boat. When the bucket is lowered over the jet, it blocks the jet and reverses its direction, causing the boat to move backwards. If the bucket is only partially lowered, it reverses some of the jet, thereby reducing the forward thrust, but does not reverse the direction of the boat""s motion. If the bucket is lowered to reverse approximately half of the jet, then a balance point is achieved, and forward thrust of the boat is eliminated.
Some waterjet boats also have a third steering element, called a bowthruster, for side to side movement at low speed. The bowthruster is typically a tube that runs laterally across the boat near the bow, below the waterline. A reversible propeller in the middle of the tube can thrust the boat in either sideways direction.
Waterjet boats have a number of advantages over traditional propeller driven boats, including reduced noise and low draft. Waterjet boats, however, can be notoriously difficult to control, particularly at low speeds, e.g., when docking. In prior art waterjet boats, maintaining a heading and adjusting course, particularly at very low speed, requires considerable training, especially for operators accustomed to traditional propeller boats.
To facilitate steering of boats in the open sea, some boats include autopilots. The autopilot, when activated by an operator, maintains the boat""s current course. Some propeller boats also include a detent structure to lock in a boat""s course. In these boats, the steering wheel includes a notch or a groove, and the mechanism steered by the wheel includes a corresponding notch or groove. When the pilot returns the wheel to a neutral position, the corresponding notch and groove engage, holding the wheel in the neutral position. In certain boats, the autopilot automatically engages when the pilot returns the wheel to the neutral position and the corresponding notch and groove engage.
We have discovered new ways to use an autopilot to both steer and maneuver a boat, particularly a waterjet boat.
In the improved steering system, a specially integrated autopilot remains engaged unless the operator is actively commanding the boat to change course. The operator need not constantly engage and disengage the autopilot, as is necessary with a conventional system. For example, in a boat in which steering is performed using a joystick, course changes can be effected simply by moving (e.g., twisting) the joystick. That movement automatically disengages the autopilot, allowing the operator to achieve the course change. When the operator has completed the course change and released the joystick, a centering spring returns it to a neutral position and the autopilot automatically reengages.
The new steering system is simpler to use than conventional systems as the operator does not have to be concerned with manually disengaging and then re-engaging the autopilot. The autopilot functions in the background without the operator ordinarily needing to give it any attention. The system is also safer, as an instinctive steering correction to avoid an obstacle will immediately disengage the autopilot.
In the improved maneuvering system, the autopilot is used for controlling the direction of a waterjet boat during very low speed (e.g., less than 4 knots) maneuvers, such as docking. The autopilot controls the steering system, e.g., rotation of the waterjet nozzle, to maintain a desired bow direction, while the operator uses a manual control device to apply a sideward force (e.g., from a bowthruster) to move the boat sideways. Preferably, a stick control device (e.g., a multi-axis joy stick) is used, and movement of the stick in a selected direction (sideways, fore and aft, or a combination) causes the boat to move in a corresponding direction, but with the direction of the bow maintained by the autopilot.
This new maneuvering system makes it possible for even a novice operator to easily maneuver a waterjet boat in close quarters. The unsettling effects of wind and tide on the direction of the boat are automatically compensated for by the autopilot. And the operator is able to move the boat in and out of a slip, or to and from a dock, simply by making intuitive movements of a stick control device.
In this maneuvering mode, the autopilot""s P factor (number of degrees of nozzle rotation for each degree of sensed heading error) is preferably set higher than would be used when the boat is underway. For example, P factors greater than 4 (and more preferably greater than 6) have been found to work successfully on a 35 foot Hinckley Picnic Boat powered by a single waterjet drive.
A simple and effective implementation of this maneuvering system is to use a bow thruster to apply sideward force in response to operator movement of the stick control device. The bow thruster initially changes the direction of the bow, but the autopilot quickly corrects the directional error by producing a compensating rotation of the waterjet nozzle.
Used in combination, the steering and maneuvering aspects of the invention make it possible to leave an autopilot constantly on, from first turning on a boat in a slip to driving the boat at high speed on open water. The new steering system works well in combination with the new maneuvering system, as if directional changes are desired during very low speed maneuvers, the operator simply moves the control device in the manner required to make a course change (e.g., twisting a joystick), and then resumes the intuitive maneuvering movements, as the autopilot will then maintain the new boat direction.
Embodiments of the invention may include one or more of the following features. The boat may be a waterjet boat, e.g., a waterjet boat less than 75 feet in length. The stick control member may be configured to rotate to the left and to the right about a generally vertical axis; rotating the stick control member to the left steers the boat to port, and rotating the stick control member to the right steers the boat to starboard. The stick control member may be biased to a neutral zero rotation position by a centering torque provided, e.g., by a spring, so that when the operator releases the stick control member, the centering torque returns the stick control member to its neutral position. The autopilot may be configured to always be engaged when the stick control member is in its neutral position.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments, and from the claims.